1. Field of the Invention
This invention relates generally to a thin film electroluminescent edge emitter structure for use as a high resolution light source, and more particularly, to a thin film electroluminescent edge emitter structure forming an array of light-emitting pixels configured to permit each of the pixels of the array to be energized utilizing multiplexing techniques. This invention further relates to an electronic drive system for use with the edge emitter structure of the present invention.
2. Background Information
It is well known that an electroluminescent device generally, and particularly a thin film electroluminescent edge emitting device, may be utilized to provide an electronically controlled, high resolution light source. One such device is disclosed in U.S. Pat. No. 4,535,341 to Kuhn et al., which is assigned to the assignee of the present invention. This patent discloses a thin film electroluminescent edge emitter structure which includes a first dielectric layer disposed on a common or bottom electrode, a second dielectric layer spaced from the first dielectric layer, a phosphor layer interposed between the first and second dielectric layers and an excitation or top electrode disposed on the second dielectric layer. At least one of the electrodes, for example, the excitation or top electrode, is segmented to form a plurality of individual control electrodes. The plurality of individual control electrodes in combination with the remaining structure form a plurality of individual light-emitting pixels. In order to facilitate the electrical connection required between each pixel control electrode and the pixel excitation source, the control electrodes are connected to edge pads disposed on the edge emitter structure-supporting substrate via conventional fan-outs.
Another example of a device which utilizes an electroluminescent light-emitting structure as a light source is illustrated in U.S. Pat. No. 4,734,723. This patent discloses an electrophotographic printer which includes an optical head formed from a plurality of electroluminescent devices positioned along one edge of a substrate. A plurality of light waveguide strips are also positioned on the substrate in association with the electroluminescent devices. It is stated that the waveguide strips serve to transmit the light from the electroluminescent devices to the other edge of the substrate which is brought into a face-to-face relationship with the printer photoreceptor. The patent is silent on an electronic drive system for the optical head and the specific connection between the optical head and drive system, other than to state that the lower electrode layers forming portions of the plurality of electroluminescent devices are supplied with electrical signals of varying amplitudes from an optical head drive to cause the associated devices to produce different quantities of light.
Japanese laid-open patent application Kokai No. 63-91998 discloses an EL luminescent edge emitter array operable as a light source in which the upperside metallic electrode wraps around the reflecting end surface of the luminescent layer. Each of the EL elements of the array is surrounded by an insulating film whose refractive index is lower than that of the EL layer. The array further includes a discharge prevention area between the bottom electrode and reflecting end of the top metallic electrode. The laid-open Japanese patent application is also silent on an electronic drive system for the array.
While the prior art discussed above disclose a thin film electroluminescent edge emitter structure for use as a high resolution light source, only the edge emitter structure of Kuhn et al. discloses fully functional means for connecting each of the individual light-emitting pixels of the structure to a pixel excitation source. Recognizing that the physical size of each light-emitting pixel of the structure is extremely small, Kuhn et al. teach the use of a fan-out to connect the control electrode of each pixel to an edge pad spaced a substantial distance from the structure itself. Each of the edge pads is, in turn, connected with the pixel excitation source. Thus, the fan-outs and edge pads provide a signal flow path between the pixel excitation source and the control electrodes of the individual pixels forming the edge emitter structure. Although the fan-outs and edge pads provide a satisfactory means for connecting the excitation source with each of the pixels of the edge emitter structure, forming the fan-outs of the size and length required is a physically complex task and requires a relatively large area for fan-out expansion. As a result, the substrate layer upon which the edge emitter structure, fan-outs, and edge pads are positioned must be physically large to accommodate this fan-out expansion.
Generally, therefore, there is a need for an improved thin film electroluminescent (TFEL) edge emitter structure requiring fewer physical connections between the individual pixels forming the structure and the pixel excitation source than TFEL edge emitter structures heretofore known and utilized. Specifically, the improved TFEL edge emitter structure must be configured to permit the individual pixels of the structure to be selectively energized utilizing multiplexing techniques. Forming a structure wherein each of the pixels of the structure may be selectively multiplexed to an "on" or "energized" state results in an edge emitter structure having a physical size smaller than the combination edge emitter structure/fan-out arrangement of the prior art, and further results in a TFEL edge emitter structure capable of being easily manufactured and readily mass produced. In addition, there is a need for a novel electronic system for driving the multiplexed TFEL edge emitter structure of the present invention to permit the individual pixels of the structure to be selectively energized.